"The second was wearing dark jeans, a dark jacket, a dark beanie hat and dark shoes. The third was over 6ft and was wearing a dark beanie hat, a dark jacket, dark jeans and dark footwear. The fourth man was of mixed-race appearance with a slim build and was wearing a black beanie hat, dark jeans and dark shoes."

Police are appealing for witnesses, particularly the occupants of a vehicle travelling along Upper Cross Street very shortly before the incident and who may have seen the car mentioned above.

Witnesses, or anyone with information, are asked to contact Northamptonshire Police on 101. Alternatively, they can call independent charity Crimestoppers anonymously on 0800 555111.